l. Field of the Invention
This invention relates to a heat-developable light-sensitive material, particularly, a heat-developable light-sensitive material capable of providing an image having a black color tone.
2. Description of the Prior Art
The photographic process using a silver halide is the most commonly used photographic process, since this process is superior to the electrophotographic process or the diazo-photographic process in photographic properties such as sensitivity and gradation. However, the silver halide light-sensitive material used in this process is imagewise exposed, developed with a developer and, furthermore, subjected to several processings such as stopping, fixing, water washing and stabilizing to prevent the developed image from discoloring or fading and the non-developed area (which will hereinafter be referred to as "background") from blackening. Thus the photographic process using a silver halide has a disadvantage that much time and labor are required for the processing, the handling of the chemicals is harmful to the human body and the processing rooms and the hands and workers' clothes are stained. Therefore, it has been very desirable to improve the photographic process using a silver halide so that the processing can be carried out under dry conditions without using solutions and so that a stable processed image can be obtained. Many efforts have been made to this end.
One proposal is to use a light-sensitive element consisting of a silver salt of a long chain aliphatic carboxylic acid such as silver behenate, silver saccharin or silver benzotriazole, as a main component, and a catalytic amount of a silver halide, as disclosed in U.S. Pat. Nos. 3,152,904, 3,457,075 and 3,635,719 and British Pat. Nos. 1,163,187 and 1,205,500.
The present invention is concerned with a heat-developable light-sensitive material of this kind. In the heat-developable light-sensitive materials which have hitherto been proposed, for example, compositions comprising a silver salt of a fatty acid, a reducing agent and a catalytic amount of a silver halide, an image obtained after imagewise exposure and heat development has a light brown color tone. Therefore, the contrast between the image area and the non-image area is too low. In order to increase the contrast, it is thus desirable to increase the color density of the image and to provide a black color tone to the image.
U.S. Pat. Nos. 3,080,254 and 3,107,174 disclose that phthalazinone is effective for increasing the color density of an image, as a color toning agent. However, phthalazinone has the disadvantage that the developing apparatus is often damaged by sublimed phthalazinone and the cost of producing the light-sensitive material increases because phthalazinone is expensive. Various efforts to seek excellent color toning agents in place of phthalazinone have been made and, for example, some compounds are disclosed in U.S. Pat. No. 3,846,136.